Abstract

During the summer of 2009 our research team conducted a pilot study that focused on the capture and diagnostic sampling of wild Bonnethead (Sphyrna tiburo) and Atlantic Sharpnose (Rhizoprionodon terraenovae) sharks. These two species are commonly found in the coastal southeastern United States, where they reside in shallow water and enter bays and estuaries. The Bonnethead feeds on crustaceans and mollusks, while the Atlantic Sharpnose consumes small fish, mollusks, and shrimp.^1,2 These two sharks rank in the top 6 species captured by commercial and recreational fisheries off the coasts of Georgia and eastern Florida.³ Neither species is currently designated threatened or endangered, thereby increasing the need to obtain baseline data regarding their overall health. To date, we have collected samples from 16 Bonnethead and 17 Sharpnose sharks and performed complete blood counts (CBC), plasma biochemical profiles, plasma vitamin A/E/D, plasma nutrient trace minerals, and plasma osmolarity analyses. The most notable finding from this preliminary work is that the plasma vitamin A and E levels in our wild-caught sharks are much lower than those previously reported in a limited number of captive specimens (Table 1).⁴ Spinal deformities have been described in captive sharks ^4,5 and it is possible that hypervitaminosis A is playing a role in these deformities. Pathological findings that accompany the spinal deformities include enlarged, yellowish liver, mucosal erosions in the stomach, diffuse hyperemia and hemorrhage on the intestinal mucosa, and fibrosis of the epaxial muscles.⁴ Similar post-mortem findings are seen in vertebrates diagnosed with vitamin A toxicity. There are also several significant species differences in the plasma trace nutrients. Compared to the Atlantic Sharpnose the Bonnethead shark had higher levels of magnesium, chromium, cobalt, copper, selenium, arsenic, strontium, and silver. The other trace nutrients we measured included calcium, iron, nickel, zinc, and molybdenum, though we found no significant species differences in these plasma trace nutrients. See Table 2 for the mean for each species. There are significant species differences in the CBC data. The Bonnethead shark had a higher packed-cell volume (p=0.015) and neutrophil count (p=0.001). It should be noted that the Atlantic Sharpnose blood did not contain any neutrophils. The Atlantic Sharpnose have higher eosinophil counts than the Bonnethead (p=0.001). We believe these species differences are related to the variation in habitat use and foraging ecology of the Atlantic Sharpnose and the Bonnethead shark.

Table 1. Concentrations presented here are in µg/mL.

The data from Sharpnose (n=17) and Bonnethead (n=16) were obtained over the summer 2009 by these researchers (unpublished).

Table 2. Descriptive statistics of plasma nutrient trace mineral values of Bonnethead (n=16) and Sharpnose (n=17) sharks captured off the coast of Georgia and Florida.

All values are represented in parts per million (ppm).

Acknowledgements

The authors wish to thank the crew of the R/V Georgia Bulldog Dr. Al Dove, and everyone at the South Carolina Department of Natural Resources who helped in the collection and processing of the wild-caught sharks.

References

1.  Bethea DM, Hale L, Carlson JK, Cortes E, Manire CA, Gelsleichter J 2007. Geographic and ontogenetic variation in the diet and daily ration of the bonnethead shark, Sphyrna tiburo, from the eastern Gulf of Mexico. Mar Biol 152:1009-1020.

2.  Loefer JK, Sedberry GR 2003. Life history of the Atlantic sharpnose shark (Rhizoprionodon terraenovae) off the southeastern United States. Fish Bull 101:75-88.

3.  Trent L, Parshley DE, Carlson JK 1997. Catch and bycatch in the shark drift gillnet fishery off Georgia and East Florida. Marine Fisheries Review 59:19-28.

4.  Preziosi R, Gridelli S, Borghetti P, Diana A, Parmeggiani A, Fioravanti ML, Marcer F, Bianchi I, Walsh M, Berzins I 2006. Spinal deformity in a sandtiger shark, Carcharias taurus Rafinesque: a clinical-pathological study. J Fish Disease 29:49-60.

5.  Hoenig JM, Walsh AH 1983. Skeletal lesions and deformities in large sharks. J Wildlife Disease 19:27-33.